Heterocycles that contain nitrogen atoms are often found, e.g., in bioactive compounds and are, thus, interesting for medicinal chemistry. 1,3,4-Oxadiazoles, for example, are often present in pharmaceutically active molecules. New methods for the synthesis of these five-membered heterocycles would be useful. In particular, the photocatalytic synthesis of these compounds is still challenging. TiO₂ could be a useful catalyst in this context, but pure TiO₂ suffers from drawbacks in the light that can be used (usually UV radiation) and in its reactivity. Composites in which TiO₂ nanoparticles are immobilized on a suitable support could solve these problems.

Matías Blanco, José Alemán, Universidad Autónoma de Madrid, Spain, and colleagues have immobilized TiO₂ nanoparticles on graphene acid (GA) to obtain a composite photocatalyst (simplified structure pictured) for the synthesis of 2,5-disubstituted 1,3,4-oxadiazoles. The team first prepared GA via an exfoliation and reaction of fluorographene with a cyanide source, followed by hydrolysis. Then, Ti(OⁱPr)₄ was used as a precursor for the desired TiO₂ nanoparticles. It was mixed with GA and subjected to hydrolysis to obtain the desired composite catalyst.

The researchers used the prepared heterogeneous photocatalyst in the synthesis of biologically relevant 1,3,4-oxadiazoles from ketoacids and hydrazides under visible light. The catalyst showed improved photoactivity compared to “bare” TiO₂ and provided access to a wide range of oxadiazoles. It was recyclable and could be used for more than five reaction cycles.

• A Graphene Acid – TiO₂ Nanohybrid as Multifunctional Heterogeneous Photocatalyst for the Synthesis of 1,3,4-Oxadiazoles,
  Martina Sciarretta, Mariam Barawi, Cristina Navío, Víctor A. de la Peña O’ Shea, Matías Blanco, José Alemán,
  ACS Appl. Mater. Interfaces 2022.
  https://doi.org/10.1021/acsami.2c07880